Wood preservatives are commonly used to protect wood from fungal and insect attack. Chromated copper arsenate (CCA) was used as a wood preservative from the mid-1930's until recent times. Recently, concerns were raised about safety and health effects of CCA and its use was voluntary discontinued for residential applications in 2002. Since this time, the US wood preservation industry focused primarily on the use of water-soluble, copper based preservatives.
The soluble copper based preservatives are aqueous solutions that contain soluble copper in the form of a copper-amine complex, a copper alkanolamine complex, or a copper ammonium complex. The soluble copper based preservatives typically contain at least one additional co-biocide in order to protect the wood from various copper tolerant brown rot fungi. Exemplary commercial formulations are Copper Azole (CA), Ammonical Copper Quat (ACQ), Copper HDO (CX) and Copper Naphthenate (CuN—W). However, the rising costs of alkanolamines coupled with relatively high water leachability of soluble copper from the treated wood products have resulted in a need in the industry for alternatives to soluble copper based wood preservatives.
One alternative to the use of water-soluble copper is to use copper in an insoluble form, such as in the form of submicron or micronized particles. Illustratively, U.S. Patent Applications 2006/0062926, 2005/0255251 and 2004/0258768, the disclosures of which are incorporated herein by reference in their entireties, describe methodology for making submicron-sized biocidal particulate slurries, such as particulate copper slurries, and their use as wood preservatives.
Although micronized copper wood preservatives provide a less expensive and a less leachable alternative to the use of soluble copper, it has now been found that using micronized copper to treat wood has a significant drawback. Specifically, the surface of the wood tends to exhibit an undesirable “chalky” appearance. As used herein, the term “chalky” refers to a powdery green residue appearing on the surface of treated wood. This chalking phenomenon is particularly exacerbated in certain areas of the treated wood surface, such as the heartwood portions that lack sufficient pore structure to allow penetration of the micronized copper particles into the wood, resulting in a “blotchy” uneven appearance of residue on the surface of the treated wood.
Certain compositions containing insoluble copper particulates and amines have been disclosed in the art. Illustratively, published U.S. application 2004/0258768 claims in claim 64 thereof a composition comprising a plurality of first particulates comprising at least 20% of a sparingly soluble copper salt suspended in an aqueous carrier comprising less than 1% by weight of alkanolamines and less than 1% by weight of ammonia. Paragraph 0170 of this publication discloses a slurry comprising a liquid carrier; injectable solid particulates comprising one or more organic biocides; and one or more soluble copper salts or complexes including the soluble copper treatments described in the prior art. Paragraph 0195 of this publication discloses such a liquid carrier comprising soluble copper, such as for example copper monoethanolamine carbonate complex.
Likewise, published U.S. application 2006/0062926 discloses a wood preservative slurry containing particles of a sparingly soluble copper salt. Paragraph 0115 of that publication discloses that the slurry can additionally comprise soluble copper-amine compounds, such as ammoniacal copper, copper-monoethanolamine complex, or a copper ethylenediamine complex; however, care should be taken to insure that the pH of the slurry does not approach the range where copper amine may precipitate, e.g. at about 7.5 or at about pH 13.
Although the problem of chalking associated with micronized copper treatment of wood has now been recognized, the art doesn't disclose or suggest any means to avoid it, to the knowledge of the present inventor. The present invention provides one solution to the problem.